Limit switch



Ian. 3, 1925.

H. M KAY LIMIT SWITCH Filed Aug. 8, 1923 Hewwem 2 Patented Jan. 13,1925.

UNETE fiTATE HEUBERT MCKAY, OF SEATTLE, VIASHINGTON.

LIMIT SWITCH. i

Application filed. August 8, 1923. Serial No. 656,320.

To all whom it may concern:

Be it known that I, HEUBERT MCKAY, a citizen of the United States ofAmerica, and resident of the city of Seattle, in the county of King andState of Washington, have invented certain new and useful Improvementsin Limit Switches, of which the following is a specification.

My invention relates to a limit stop and is particularly designed foruse in connection with the engine or motor which is employed to operatepumps or like apparatus which it is desired to operate for aconsiderable period and then stop.

It is an object of my invention to provide such a limit switch which canbe set at will for operation of the engine or motor through a givenperiod of time, and which will then automatically break the controllingcircuit to stop the operation of the motor or engine, thus to obviatethe necessity of the operator being present or leaving other duties tomanually stop its operation.

A further object is the provision of a simple and conveniently operatedswitch of this type.

A further object is the provision of means in such a switch which willprevent damage to the mechanism in case the switch fails to break thecircuit or stop the operation of the engine or motor.

' A further object is the provision of a switch of this sort andmechanism for controlling the same whereby the switch may readily bedisconnected from the automatic mechanism to permit manual operationthereof, and further, a mounting for the switch which will permit suchdisconnection and which will maintain the switch in accessible positionand shielded against short circuiting or damage from oil or grease whichis necessarily associated with the automatic mechanism.

Other objects, and especially those re lating to structural details, maybe ascertained from a study of the accompanying drawings, in which myinvention is shown in its present preferred form, and of the presentspecification and the claims terminating the same. 1

My invention comprises those novel parts which are shown in theaccompanying drawings, described in the specification, and particularlydefined by the claims terminating the same.

Figure 1 is a plan View of my mechanism, the casing enclosing the samebeing shown in section and certain parts above the line of section beingomitted.

Figures 2 and 3 are transverse sections through the automatic limitingmechanism, showing parts respectively in operative and inoperativepositions.

As stated above, I intend my device to be used for such purposes as forcontrolling the operation of a pump on a farm, wherein it is desired tooperate the pump for perhaps three hours and then to stop its operation.The pump in such case might be operated by an internal combustionengine, including an ignition circuit, or by an electric motor. Ineither case the switch meme here 2 and 20 may be included either in themain circuit of the engine or motor or in a control circuit. The mannerof connection of these switch members is unimportant. I have shown apulley 10, which is connected to rotate a screw 1 through suitable speedreduction means. The pulley 10 is intended to be connected in somesuitable manner to be driven by the motor or engine which drives thepump, in the illustration given above. Thus it will be seen that so longas the motor or engine driving the pump is. operative, the screw 1 willrotate, and as the switch members 2 and are in the control circuit ofthe motor or engine, it follows that the screw 1 will rotate solong asthe switch members 2 and 20 are in contact.

The exact drive connection between the pulley 10 and the screw 1 isimmaterial, although I prefer that it should include pulleys 11 and 12connected by a belt 13. By this means, or its equivalent, it is possibleto vary the speed ratio between the pulley 10 and the screw 1 toaccommodate a given limit switch mechanism to engines or motors ofdifferent speeds. This is done by varying the relative diameters of thepulleys 11 and 12.

The speed reduction gearing and the screw 1 which it drives, arepreferably enclosed within a casing 3 upon which fits a cover 31. Withinthis casing 8 I mount a carriage 4 which is movable towards and from thescrew 1 and is provided with threads 41 which are complemental to andengageable with the threads of the screw 1. Such movement of thecarriage towards and from the screw may be secured in a variety of ways.For this purpose I have shown a ,pin" 47.

the carriage at reachesthe end of its'normal travel the spring 24-willpull upon the switch guide rod42, j ournaled in the casing 3 uponeccentric bearings 43. By rotating the rod 42 upon these eccentricbearings 43, as by means of a handle 4%, thecarriage t is reciprocated.

I have shown a handle connected to the carriage 4 and projecting througha slot 34 in the casing 3. A bar 4E6-secured to the carriage within thecasing is visible through anenlargementt? of the-slot 3st and may hegraduated in proper units, as of time, corresponding to the rate oftravel of the carriage 4: when its threads are engaged with thescrew. 1. The carriage t can thus be set at'any position lengthwise ofthe screw 1 whenits threads all are disengaged therefrom by means of thehandlef tti, and the length of time which will be requi: ed to advancethe carriage to the'end otits normal travel, by means 0t rotation of thescrew 1', can be determined by-ret'erence to the gageorscale bar 46,visible through the enlarged index opening 35.

Associated with the carriage l are means for controlling the position ofthe switch members 2 and 20: I have shown the switch member 20 asmounted upon the cover 31. and the.member 2 as carried upon a bell crankarm 21 pivotedat 23 uponthe cover 31. 1 One arm'of the lever '21 extendswithin the casing 3 where it is engageable with a pin'4c7carried by thecarriage 4,. The length ofthis pin 47 is so proportioned relative to theposition otthe'bell-cranlclever 21 and the screw 1 that whenthe'carriage 4 reaches the end of its normal travel upon the screw 1,theswitchfarm'21 willpass beyond the end of'the'pin 47. A spring 2e maybe secured to an arm-25 secured upon the shaft 23' whiclrcarriesith'eswitch arm 21, and anchored'atrrts other end to the cover 31 or'to thecasing "8/ By this means the switch members 2 and 20 tend constantly tobe separated but may. 'be held closed against the tendency of the spring24 by means of the Itwill be evidenflthen that when arm, and the latter,being unsupported then "by the Pilit'l, will permit the switch members 2and 20to' be separated, thus to break the controlling circuitot themotor or engine.

I have shown the end of the screw 1 re- "duced, as shown at This pliesbeyond the normal end of travel otthe carriage 4. If it should happenthat the-switch'members 2'and' 20' should not be separated when thecarriage reaches the end of its normal travel, or if' for some otherreason the motor or engine-should"fail to-stop, its continued operationwould carry the carriage l beyondthe-end of the screw l to the cut-away-por-. tion 15. lvhile the screw would continue to rotate, it would notthen produce any th'ereto' and engageable'therewith, means for furthermovement of the carriage 4t and the mechanism consequently would not bedamaged.

It is believed-that; it will be obvious from the above description howthe carriage 4, by disengagement trom the screw 1, may be adjustedlengthwise thereof and set to operate tor agiven period of time, and howat the end of that period of time the switch members 2 and 20 will beseparated to stop theoperation of the motor or switch. I will,therefore, not go into further detail regard ing the-operation ot thedevice.

.Vhat I claim as iny invention is: 7

l. A limit switch comprising, in combination with a pair of switchmembers normally tending to be separated, a screw rotatable whilesaid'switch is closed, a carriage havcarriage tor-holding said switchmembers closed until the carriage reaches the end" of its normal travel,andmeansfor moving saidca -riage atwill towards the screw to engage itsthreads therewith, or awaytrom the screw to permit adjustment of theposition of the carriage lengthwise of the screw.

3. In combination with a pair of switch members normally tending'to beseparated, a screw rotatable while said switch is closed, a carriagehaving threads complemental thereto and engagealole therewith, meanslupon said carriage for holding said switch members closed until the]carriage-reaches the end of its normal travel, a rod guiding saidcarriage for movement lengthwise ot the screw and eccentric bearings torsaid: guide rod, whereby the carriage may be moved at will'towards thescrewto permit manual movement of the carriage lengthwise of the screw.J

4. In combination with'a pair-of switch members norm ally tending to be.separated, a switch arm carryingone of said members, a screw rotatable''whiles aid switch is closed, a carriage movable towards and from thescrew and having threads] complementat moving said carriage towards'oraway from thescrew to engage its threads therewith or disengage them:therefrom, respectively, and a pin movable with said carriage andengageable bysaid-switch arm, andf'of a length to support the latteruntil the carriage reaches the end of its normal travel.

5. In combination with a pair of switch members normally tending to beseparated, a screw rotatable while said switch is closed, limit meansincluding a threaded member engageable with said screw for retainingsaid switch members closed, and operable through said screw to releasethe switch members after a predetermined period of operation, and thethreads of said screw being cut away at a point beyond the position ofthe threaded member at the normal releasing position.

6. In combination with a casing and a removable cover therefor, a switcharm pivotally mounted upon said cover a pair of complemental switchmembers, one upon said arm and the other upon said cover, means withinsaid casing having a bearing engagement with said switch arm, andoperable to permit separation 01' the switch members following apredetermined period of operation, said means and the switch arm beingdisengageable upon removal of said cover.

7. In combination with a casing, a switch arm supported from and movablerelative to said casing, and projecting therethrough, a pair of.complemental switch members, one upon the outer portion of said arm andthe other upon the outside of said casing, means tending to move saidswitch arm to separate said switch members, and means within said casingengageable with the inner end of said arm to maintain said switchmembers in contact, and operable to permit separation of said switchmembers following a predetern'iined period of operation.

8. A device as in claim 7 including a removable cover for the casing,the switch arm and its associated parts being mounted on said cover andthe arm projecting therethrough, said means engaging the inner end ofthe switch arm being fixed within the easing, and being disengageablefrom said arm to permit separation of the switch members upon removal ofthe cover.

9. In combination with a control arm normally tending to move to aninoperative or stop position, a screw rotatable while said arm remainsin operative position, a carriage having threads complemental to thescrew and engageable therewith, and means upon said carriage for holdingsaid arm in operative position until the carriage reaches the end of itsnormal travel, said means and the arm being thereupon disengageable topermit movement of the arm to normal inoperative position.

Signed at Seattle, King county, VVashington, this 31st day of July, 1923HEUBERT MoKAY.

